The present invention relates to metal "wood" golf club heads and more particularly to a head construction which reduces deflection of the face plate during ball strike and increases the head and face plate rigidity for greater ball velocity.
Currently, most golf club heads of the type called "woods" are of hollow construction, some being fiber-reinforced plastic and most being cast of metal. In general, it is desirable to make these heads as large as practical, but this is limited because the walls tend to become too thin for manufacturing and the structure of the head becomes too fragile for the large momentary loads. In addition, greater structural rigidity of the club head increases the velocity of the ball.
Presently, metal wood heads are commonly cast, usually using stainless steel, with thin walls, a somewhat thicker face, and a large hole, usually in the bottom. A thin sole plate is welded into this hole to complete the structure of the cast metal wood head. These are generally called "metal woods". This invention is also applicable to "wood" club heads made of fiber-reinforced composite construction, but not to club heads made of solid construction such as wood or plastic and is equally applicable when the wood is fabricated as a hollow structure, using other materials such as graphite fiber-reinforced plastic.
Most heads of hollow construction are filled with foam. Such foam filling is of negligible structural importance and is of value for controlling the sound of impact, for making small final adjustments of head weight, and the like.
Metal wood heads are essentially a hollow structure with wall thickness of about 0.040 inch and face thickness of about 0.10 to 0.12 inch. The larger the volume of this structure, the greater the values of the mass moments of inertia about all axes of rotation. This decreases the detrimental effects on direction and distance for off-center hits. The maximum volume is limited because increasing the volume much beyond the usual amount requires an unacceptable increase in weight or else a thinner wall construction which becomes too fragile to survive the remarkably large impact forces or too thin for satisfactory casting.
During impact, the golf ball momentarily flattens against the club face, forming a circular contact area having a diameter of about three fourths of an inch. The surface of the club head also deflects but much less because the head is always made of much more rigid construction than the ball. Energy is required to deform the ball and the club head. If this energy of deformation (potential energy) is not completely transferred back to velocity energy (kinetic energy) during the impact, the ball will leave the club with correspondingly reduced velocity. A more rigid construction of the club reduces this problem because it deforms less and stores less potential energy. If it were perfectly rigid and did not deform, the problem would be eliminated so far as the club head is concerned. Deformation of the ball is, of course, a different and separate problem from club head design.
The problem of rigidity of the golf club head has been recognized in the prior art and attempts have been made to increase the rigidity without greatly affecting the weight of the club head. For example U.S. Pat. No. 4,076,254 to Nygren discloses corrugated metal ribs on plates 28 that extend from the rear of the face plate rearwardly to a weight. These plates are secured to the face plate with a suitable adhesive and are in a central area of the face plate and while the plates extend fore and aft (toe to heel) a substantial amount, the uppers edges of the face plate are not supported and an off center shot in up and down direction will cause substantial deformation of the club face plate.
United Kingdom patent 664,438 also discloses a strut extending between a front striking face and a rear wall, which is relatively straight in load bearing direction. The strut is described as being approximately one-half the width of the face plate and positioned centrally. The strut is smaller adjacent the face plate and expands out in rearward direction.
U.S. Pat. Nos. 4,930,781 and 4,988,104 have corrugated structures that bear on the center portions of the face plate but do not have the rigidity enhancing construction of the present invention.
An internal structure of honeycomb is used to support the face in U.S. Pat. No. 4,930,781 and also in U.S. Pat. Nos. to Raymont 3,847,399, and Allen 5,060,951. These are a departure for hollow woods from the usual structure in which the curved outer shell supports most of the load. In no case, do these internal structures extend from the face all the way to such mass as may be concentrated at the rear of the head. Also, none of these designs completely replaces the curved outer shell for structural purposes.
Two other U.S. Pat. Nos., Thompson 4,313,607 and Kobayashi No. 4,811,949 show one or more internal bracing structures which reach from the face to the rear of the outer curved shell. They do not show a suitable internal brace which can completely replace the structural features of the outer curved shell.
Desboilles et al., U.S. Pat. No. 5,106,094 shows internal support structure and other unusual features which are of general interest but have little relation to the present invention.
Prior clubs do have outer shells that attach directly to the face plate edges, as shown in U.S. Pat. No. 4,438,931 but these shells are not designed to carry the load without substantial deflection.